1. Field of the Invention
The invention relates in general to an optical disk drive and the method thereof, and more particularly to an optical disk drive capable of writing a re-writable optical disk and the method thereof.
2. Description of the Related Art
When an optical disk drive records an optical disk, such as a CDRW, the optical pick-up head emits laser of a write power during write power phase and of read power during read power phase. However, the optical disk drive performs an optimum power calibration (OPC) procedure to derive required optimum power before performing related disk-write operation.
The recorded data would be crashed if the optical disk try to record data on defect regions in a CDRW. Therefore the optical disk drive should detect those defect regions on the CDRW during disk-write operation so as to prevent those defect ones from being recorded during related disk-write operations.
Conventionally, a SBAD (sub-beam adder) is employed for detecting the defect regions on an optical disk. The so-called SBAD signal, which is the summation of the servo signals A, B, C, D, E, F, G and H, is also used to assist focusing of the optical pick-up head. The SBAD signal has different levels during write power phase and read power phase since there are different power being employed during these two phases.
FIG. 1 is a diagram showing WLDON signal and SBAD signal of a conventional optical disk drive. WLDON is used to indicate the laser power at the write power phase or at the read power phase. At the read power phase R, WLDON signal is at low level, while the WLDON signal is at high level during the write power phase W. Due to the difference of read power and write power, SBAD signal has corresponding levels of Sl and Sh.
FIG. 2 is a diagram showing SBAD signal when a defect of CDRW is found, wherein the SBAD signal level decays a defect threshold when it is affected by a defect region. Obviously, area D1 is a defect found during the read power phase, and is easily detected by using the SBAD signal level. However, area D2 is a defect found during the write power phase, which is not easily detected. If the defect threshold approximately equals to the level difference (Sh-Sl) of SBAD signal, the defect at area D2 during the write power phase would be recognized as a normal portion of the read power phase. If the servo system fails to recognize and jump away the defect area D2, the disk write operation may malfunction or result in an error.